Magnesium

The long-tailed character is called Magnesium mikuo (Mg) ( 人型Mg ), he also has a humanoid form.

Design
Appears to be a Mechanize Parasite that look's like a Scorpion supporting Calne Ca

but in humanoid form he resembles short-haired Gakupo but it is not confirm on Deino's Original Characters designs

Similar to Calne CA, he is sweet and friendly but looks weird.

Biography
He was a low pitch Calcium Miku. So he is, indeed, Rubidium Mikuo.

Voice configuration
Unknown

Relationships
Creatures that are frequently seen in videos accompanying Calne Ca are a walking skull called Chibi Cal-san (ちびカルさん), now officially known as Rubidium, it is the same kind of machine as Calcium, and doesn't have a mechanical body, though has been modeled by Krystal to have a human figure in some of his images. Sometimes Calne will place a skin over the skull.[8]  The long-tailed character is called Magnesium (Mg) (人型Mg), he also has a humanoid form.[9] [10]

Calcium comics
by Deino3330 deviantART

Zeromachina
a Visual Novel created by Krystal that will come out soon.
 * Artwork
 * deviantArt Deino3330

Trivia

 * He is one of the Element Characters